Lap for truing gears and the like



Jan. 8, 1929. 1,698,214

A. w. COPLAND ET 1.

LAP FOR TRUING GEARS AND THE LIKE Original Filed April 10. 1922 2 Shets-Sheet 1 fivvewroef:

Jan. 8, 1929.

A. W. COPLAND ET AL LAP FOR TRUING GEARS AND: LIKE 2 Sheets-Sheet 2 Original Filed April 10. 1922 ATTOR/VE'K Patented Jan. 8, 1929.

UNITED- STATES ATENT OFFICE.

'ALExANDEE w. COPLAND, E BIRMINGHAM, MICHIGAN, AND MAXWELL I. MATHEW- soN, 0F PROVIDENCE, RHODE ISLAND, ASSIGNORS T0 DETROIT AND SECURITY TRUST COMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN.

LAP FOR TRUING GEARS AND THE LIKE.

Original application filed April 10, 1922, Serial No. 551,140, and in Great Britain September 14, 1926.

' Divided and this application filed March 23, 1927. Serial No. 177,742. i

The invention relates to'the art of truing gears and more particularly to that part of it which is generally known as lapping. The present application is a division of our copending application Serial No. 551,140, filed April 10, 1922.

The lapping of gears has heretofore been effected by running two or more gears in mesh with-each other and With an abrasive material between the engaging surfaces or by similar- .ly running a gear in mesh with a rack.

Where the only movement given to the gears is that of rotation about their respective axes, the results obtained are not satisfactory. This is for the reason that the grinding is only produced Where there is a slipping or sliding of one surface over another, and inasmuch as the sliding upon each other of the teeth of rotating intermeshing gears With the commonly employed involute teeth is zero at the pitch circle and'progressively increases on each side of said circle with a maximum at the crown of each tooth, it is evident that the grinding produced has a tendency to change the tooth fromits true involute form. lVith certain lapping methods a relative axial reciprocation has been imparted to the intermeshing gears, or to the gear and the rack in case a rack is employed, in addition to the relative rolling, but this is also defective and inevitably results in distortion of the true involute tooth form because the effect includes that incident to the rolling, as above described.

In such a lapping or grinding operation as last referred to, the amount of grinding or abrading of asurface sliding in Contact with another is dependent first, on the character of the abrasive material used; second, on the area of abrading surface that is moved over each unit area of the surface to be ground or I .trued; and third, the amount of pressure per unit area of contact. Accordingly, to produce uniform grinding on all portions of a surface. contacting with the abrading surface there must be uniformity in abrasive material, area. and pressure. But, as above noted, in the method in question not all of these conditions are met. v

Again, in applicants method of truing.

gears disclosed in their application Serial No. 551,141, filed April 10, 1922, a lap is provided formed with teeth oppositely disposed and complementary to the teeth of the gear and having a pitch circle substantially equal to the pitch circle of the gear. This lap and the gear to be lapped are registered with each other in the relation of axially coincident internal and external inter-meshing gears, then one is reciprocated with respect to the other in mutual abrasive Contact, and intermittently one is progressively rotatably advanced in relation to the .other to change the registration of the teeth. If the gear is a spur gear, the lap of course takes the form of an internal gear and, vice versa, if the gear to be lapped is an Internal gear, the lap takes'tlae form of a spur gear. The lap is preferably elongated axially in order to afford adequate abrasive area. In this last method, just as in the former one in Which combined rolling and sliding movements are used, the amount of grinding or abrading of a surface sliding in contact with another surfaceis dependent first, on the character of the abrasive material used second, on the area of abrading surface that is moved over each unit area of the surface to be ground or trued and third, on the amount of pressure per unit area of contact. While the last described method does not have the defect referred to in the case ofthe other method, there are instances in the use of the second method in Which it is desirable to control the amounts of material ground off from different parts of the gear to be trued.

The general object of the present invention is the provision of a type of lap suitable for. the truing of gears and the form'of which can be yaried to control one of thethree factors previously referred to, namely, the area of abrading surface moved over each unit area of thesurface to be ground or trued.

A urther and more specific object of the invention is the provision of a lap of the type referred to adapted fornse in the first described method of truing gears and capable of controlling the amounts of materials ground y different parts of the gear tooth.

Another specific object/ofthe invention is off from different portionsof the teeth of the gear to belappe'dcin a manner to automaticalcompensate for the variable slippage at The invention will be'further described in connection with the accompanying drawings in which are shown different forms of our improved'lap and diagrams designed to make clear the method of using the laps. In the drawings Fig. 1 is a diagrammatic view showing the intermeshing teeth of a spur gear and a lap in the form of a second spur gear .and indicating by the diagonal shading the relatlve widths of zones of surface which are traversed by the mating tooth during equal angular movements.

Fig. 2 is a view similar to Fig. 1 showing the tooth of a spur gear in mesh Wltll the teeth of a lap, the lap in this instance being in the form of a rack having straight sided teeth. i

Figs. 3 and 4 are respectlvely a sect1onal elevation and a side elevation of a gear 111 mesh with a rack surface forming a lap therefor, the section shown by Fig. 3 belng taken on the line ,3--3, Fig. 4.

Fig. 5 is a view similar to Fig. 3 showing a modified construction.

Fig. 6 is a longitudinal section through an annular internally toothed lap.

Fig. 7 is a cross section on the line 7-'( of Fig. 6.

Fig. 8 is a view corresponding to 6 showing a modified form of construction.

Fig. 9 is a diagrammatic view illustrating the operation of the apparatus disclosed in our aforesaid application Serial No. 551,141, which is adapted for use in the carrying out of the second of the above described methods of truing gears or the like.

Referring first to the form of lap adapted for-use in the first ofthe'above described methods of truing gears, in Fig. 1 is shown a ortion of a spur gear 1 having teeth 2, 2 of lnvolute form in mesh with correspondingly shaped teeth 3 of a lap 4:, which in this instance is in the form of a second spur gear. The relative widths of zones traversed by the mating tooth for equal angular movements of either the gear or the lap are indicated by diagonal shading on the body of each tooth.

It will be observed that "these zones vary in thickness from the root towards the crown of each tooth. It will also be observed that when two teeth are in mesh that the smallest zones on one are adjacent the largest on the other. As, for instance, zones a and 7) on the gear 1 are adjacent zones a and 7) on the lap 4. As the zones indicate the amount of surface traversed by the mating tooth for equal angular movements, the zones will have to traverse each other during a unit amount of such movement, which, due to the difference in width of the contacting zones, will result in a relative sliding between the con acting surfaces. It will also be observed that the intermediate zones are unore nearly equal. This means that the relative sliding becomes progressively less ast-he point of engagement approaches the mid portions of the respective teeth, ,with zero sliding at the pitch line. 1

It will thus be seen that this relative sliding of the tooth surfaces is greatest at the extremities ofthe intermeshing teeth and gradually decreases to zero at the pitch line. As the grinding away of the tooth surfaces occurs only where there is relative sliding it follows that during the relative rotation of a spur gear in mesh with a lap in the form of asec- 011d spur gear the contacting surfaces will be ground away more at their extremities than at the pitch line. As stated, it has been proposed to combine an axial reciprocation of either the gear or the lap simultaneously with the relative rotations, but this is also defective as the sliding which is incident to the relative rotation above noted, is still present. In Fig. 2 we have shown a portion of a spur gear 5 with a tooth 6 of involute form in mesh with the teeth 7, 7 of a lap 8 which in this case is in the form of an involute rack having straight sided teeth. 'The relative widths of the zones traversed by the mating teeth for equal angular movements of the gear to be ground are indicated by diagonal shading, as in the previously described case. It will be observed however that the zones on the rack tooth are equal in width. The relative sliding between the contacting teeth will be zero at the'pitch line, as in the first instance but the variance in the relative sliding between the contacting surfaces above and be low the pitch line is not the same as in the previously described example; however, it can be readily ascertained by comparing the widths of the zones on the adjacent surfaces ofthe intermeshing teeth. It has also been proposed to combine a reciprocation of the rack parallel to the gear axis (or an axial reciprocation of the gear) simultaneously with their relative rotation; but, as in the previous case, there will still be a difference in the. grinding effect due to the above noted sliding action incident'to the rotating movement.

If, during the relative rotation and simultaneous reciprocation of the intermeshing gear and lap, the length of the reciprocation of the lapping surfaces could be varied in inverse proportion to the amount of sli-din g incident to the rolling action, the area of abrading surface moving over each unit area of the surface to be ground could be made uniform throughout. This supposed variable reciprocation is not feasible, but if, in place of a continuous surface on the lap tooth. this surface is interruptedor cutaway with the width of the interrupt-ions varying in direct proportion to the amount of relative sliding, the same compensation may be made for the unequal width of zones with uniform lengths of reciprocation.

As illustrative of some of the different ways in which the effective grinding areaof able sliding.

the lap can be varied, we have shown in Figs. 3 and 4 a lap with its teethmodified in one way, and in Fig. 5 a corresponding lap w1th a distinctly different modification.

As shown in Figs. 3 and 4, 10 represents a gear wheel and 11 a lap in the form of a rack in relation to which the gear wheel is recipr'ocated axially while rolling in mesh therewith. Any suitablemeans may be employed for providing this relative movement between the gear and lap, such as the one shown in U. S. Letters Patent No. 1.486339, issued March 11, 1924, to W. E. Hoke. In this modification, the teeth of the rack are in t'errupted or cut away by the V-shaped channels 12. Obviously'a lap of this form willha-ve a grinding effect on the gear tooth to be lapped that progressively increases from the root of the. gear tooth toward its crown.

In Fig. 5 the arrangement of lap 21 and gear 20 is similar to Figs. 3 and 4, the difference being that the interruptions or cut-away portions 22 of the lap in this instance are dove-tailed in'shape with the width of interruption greater at the base of the rack tooth than at the crown. Obviously this construction has an opposite efiect to that shown in Figs. 3 and 4.

In utilizing our improved type of lap in truing gears by the method under consideration one first predetermines the amount of relative sliding occurring between the contacting surfaces of the particular form of gear and lap teeth involved incident to their relative rotation, and then forms the lap so that the width of the interruptions or cutaway portions will be proportionally greater at the point where the largest amount of sliding occurs and smaller where the lesser amount of sliding occurs. It will thus be seen that through the use of our method the contacting areas of the lapping surface are varied in proportion to the amount of relative sliding between the contacting gear and lap surfaces incident to the relative rotating movement, thus compensating .for that vari- In considering the action of the modified lap, it is to be borne in mind that the abrasive action is mutual, affecting the lap as well as the gear.

The method as specifically described above is applicable in instances where it is desired to produce auniform grinding-of the gear tooth surfaces. This is desirable when the original contour of the gear tooth is substantially correct, and all that is needed is a smooth finished surface. However, our invention is also applicable to instances where the original tooth surface has not been correctly formed, as for instance where there is too much material at the crown portion of the gear tooth. In such an instance the interruptions or cut-away portions of the lap tooth would be so formed as to compensate for the relative sliding referred to above and at the same time so formed as to grind away more surface at the point where the excess material occurs. In order to produce this combined action of compensating for the relative sliding and the. differential grinding the width of interruptions at the base of the lap tooth would be relatively smaller so as to present a larger area of abrading surface to contact with the crown of the tooth andthus correct the original defect in the tooth form, while at the same time, the lapping produces the smoothly finished surface desired. Thus fixed connection with the frame of the ma-v chine. A lap D, having corresponding provjections adapted to register with the gear teeth, is mounted to reciprocate vertically relative to the gear to be ground. This verti cal reciprocation is effected by means of the arm E which is connected at one end to thelap and is operated as shown by means of a suitable crank F and link F. We have shown by full, dotted, and dot and dash lines three positions of the lap I) and its operating mechanism during their travel.

In order to insure a grinding contact between the mutually engaging surfaces a torsional force is applied to the gear wheel during its engagement with the lap. The ratchet wheel G is fixed to a rotatably mounted member H which carries projections I fitting in slots formed in the member L which in turn is fixed to the arbor B which carries the gear to be ground. The ratchet wheel G is engaged by a pawl M carried by a slide N which latter is actuated by a spring 0, which in turn is actuated by a rod P. Q is a member fixed to the lap reciprocating mechanism, and is provided with a cam portion R for engaging the rod P to actuate the same to place a tension on the spring 0. The parts are so constructed and arranged that when the gear wheel is out of engagement with the lap (which occurs at each end of its stroke) no pressure will be exerted by the cam on the rod I, and consequently the spring 0 will be at zero tension. The arrangement of parts is such that as the teeth of the lap enter into.

and out of, engagement with the teeth of the gear to be ground, the inclined surfaces of the cam portion will move into, and leave, engagement with the rod P, and as a result the torsional pressure between the contacting surfaces of the gear and lap teeth will be progressively increased and decreased as 1 they are brought into and out of engagement,

respectively. It will thus be seen that during the period that the cam portion R is in operative engagement with the rod P a tersional force is being applied to the gear wheel whichwill result in the setting up of a grinding contact between the mutually engaging surfaces.

,As stated, in the operation of the apparatus as above indicated, the gear and lap move out of mutual engagement at the end of each stroke of the lap, and in carrying out the method of our application Serial No.

551,141, during such disengagement of the gear and lap we effect (by means not shown in the diagram) predetermined relative angular movement of the gear and lap, to intermittently change the registration of the gear I the tooth contours of the gear.

' ing too great fullness at the crown, or too great fullness near the root of the tooth, then the true predetermined contour desired cannot be attained by the said method. Again, in case it should be desired to effect a definite predetermined change in the tooth contour of a gear, as by removing more of the metal or less of the metal from the crown portion than from the root portion of the tooth, this cannot be accomplishediby the above described method. As will be observed from the statement of the objects of the present invention we have sought to provide an improved form of lap which is applicable to the method above described and .by use of Y which the ends last referred to above can be attained. I

Referring first to the form of lap shown in-Figs. 6 and 7, it will be noted that the lap D is, generally speaking, in the formof an axially elongated internal gear having its cylindrical body 31 formed with internal teeth 32. These teeth 32 are interrupted circumfcrentially by series of grooves 32, 32, which grooves are relatively narrow at the .roots of the teeth 32 and widen toward the inner ends or crowns of ihe teeth.

' \Vhen a spur "ear is lapped in register with a lap of this character and by the method above described. it will be seen'that the grindingefie'ct on. the sides of the gear teeth is progressively less from the roots of said teeth toward the crowns thereof than if the teeth of the lap were not grooved or cut away. The lap of this special form thus makes it possible to (1) true the teeth of gears which are too thick near'their crowns or (2) reduce the thickness .of the gear teeth near their crowns to a value less than the normal or true thickness.

By varying the form of the interruptions or grooves cut in the teeth of the lap various modifications of the lapping action may be secured. For example in Fig. 8 is shown a lap D" having'its longitudinal internal teeth 34: interrupted by a series of circumferential grooves 34; which are wider near the roots of the lap teeth and gradually 'grow narrow towards the crowns of said teeth. Obviously the effect of grooves of this character is to lessen the grinding action of the lap uponthe sides of the gear teeth near their crown.

Various other modifications of lap teeth may be used and by predetermining the form of the lap desired correction in the tooth form of the gear can be obtained. Thus, with our improved form of lap gear teeth of given contour can be modified to a predetermined contour as well as being corrected in spacing, with a minimum amount of lapping. In considering the action of the modified lap,

it is to be borne in mind that the abrasive It W11]. be understood that the forms of construction shown and described are. presented fortpurposes of explanation and illustration an can be varied widely within the scope of the appended claims.

What we' claim is:

' 1. A eylindric lap having axially elongated teeth the radial faces of which are cut away to an extent decreasing as the distance from the root to the crown of the teeth increases. 2. A hollow lap having internal axially elongated teeth, the length or axial dimension of the radial faces of which varies with the distance from the axis.

3. A lap for grinding gears and the like comprisi'ng'a body portion, and a series of equally spaced laterally elongated teeth projecting from the said body portion and adapted to be meshed with the corresponding equally spaced teeth of the gear to be ground, the said lap teeth having their faces partially cut away to an extent decreasing as the distance increases'from the roots toward the crowns of said teeth.

our signatures.

ALEXANDER w. COPLAND.

"MA WE L I. MATHEWSON. 

